Hydraulic control circuit with unloading means



Sept. 23, 1958 HYDRAULIC CONTROL CIRCUIT WITH UNLOADING MEANS Filed Dec.

R. E. scHwARY 2,852,918

5 Sheets-Sheet 1 SUMP INVENTOR Rober BSchwarg ATTORNE YQ Fie. l

Sept. 23, 1958 R. E. scHwARY 2,852,918

HYDRAULIC CONTROL .CIRCUIT WITH UNLOADING MEANS Filed Dec. 24, 1954 3Sheets-Sheet 2 i i 59 'fmf 6.1 15 54 l /66 61'? 1w; O 65 6g' 56 1f 6l a66 59 l l l j I j ll MOTOR 12J PUMP INVENTOR F162 Roberc E Schwary BYA9452/ fw ATTORNEYS SePt- 23 1958 R. E. scHwARY 2,852,918

HYDRAULIC CONTROL CIRCUIT WITH UNLOADING MEANS United States Patent()HYDRAULIC CNTRQL ClRCUlT WITH UNLGA-.DlNG MEANS Robert E. Schwary,Euclid, Ghia, assigner to The New York Air Brake Company, a corporationNew Jersey Applicatioanecember 24, 19754, sont Ns. 477,512

s Claims. (ci. news2) This invention relates to automatic transmissions.Speciiically it concerns a transmission which includes an hydraulicmotor connected to be driven by one or more of a plurality of pumpswhich are connected -in parallel between a `sump and the motor. Valvemeans are provided which provide initial sequential loading of thepumps.` A valve responsive to back pressure in the motor `inlet unloadstherpumps sequentially as the back pressure increases whereby the loadis carried by the remaining pumps. The remaining pumps, sincetheytreceive the entire outputof the prime mover, can deliver Vagainst ahigher back pressure wherebythe motor can overcome a nected to the opencenter whereby the vehicle may coastV or be pushed against low internalresistance. The control valve may be moved toeither of two operatingpositions, themotor moving in opposite directions depending upon theselection` between these two positions.

It is desirable in a system in which a gasoline engine is used that themotor be `started with the pumps unloaded. The valve means whichinitially loads thepumps assumes a position, when the prime mover isstopped, in which the discharge from. the pumps is connected to theSump. These discharge connections are provided with restrictions and asengine speed increases the back pressure between the restriction and thepump discharge is increased. The valve means are shifted in response tothis rising back pressure to direct pump flow toward the control valve.Preferably the pumps are loaded sequentially by this valve means. i

An unloading valve is provided which is actuated by back pressure inexcess of a predetermined amount to divert discharge oW from one of thepumps toward the sump. i

A preferred embodiment of the invention will be described having`reference to the accompanying drawings. Figures l and 2 placed side byside from left to right in the order stated comprise a diagram, certainparts being in axial section, of a complete circuit according to theinvention.

Figure 3 is an axial section of a modified form of the invention.

`For purposes of illustration, all of the ports and pipe connections`are shown` lying in a single plane. Obviously in the `actual apparatusthese need not be coplanar. In the specification all statements ofdirection refer to the apparatus as shown inthe drawings.

` Thesystem includes pumps 11 and 12.which comprise a idual unit,driven` by a single prime over, notshown. Pumps 11 and 12 haveitheirinlets connected in parallel ricc and draw fluid from the sump 13 anddeliver it to the valve 14 through parallel connected outlets. The pumps11 and 12 are of the constant-delivery, positive displace ment type.Pump displacement is therefore a function of the speed of the primemover. Fluid from the pump 11 is directed from the valve 14 directly tothe open* center control Valve 15. Fluid from the pump 12 is supplied tothe open-center valve 15 through the diverting or unloading valve 16.The valve 16 is pressure actuated by back pressure `and connects thepump 12 to the sump when the back pressure exceeds a predeterminedamount. The open-center valve 15 controls uid flow to the reversiblerotary motor 17.

The valve 14 includes a ported valve seat bore 18. Two hollow plungervalves 19 and 21 are slidable into bore 18 and spring biased to thepositions shown. To the right of its mid-point the `bore is encircled bythree annular grooves 22, 23, 24 which are respectively connected to thesump 13, pump 11 and to open-center con trol valve 15. To the left ofits midpoint bore 18 is encircled by grooves 25, 26 and 27 respectivelyconnected with sump 13, pump 12 and valve 16. The sump connections areprovided with adjustable restrictions such as needle valves 28. Theplunger valves 19 and 21 are mirror duplicates. Referring to valve 19,it will be seen that it is provided with three sets of radial ports 29,31 and 32. An encircling groove .33 is formed in plunger valve 19 andinterconnects ports 31 and 32. Adjacent ends of the hollow valveplungers are closed, and the space 34 defined between themis connectedwith the sump 13 as shown in the drawings.

Valve 16 comprises a body having a bore therethrough closed at oppositeends by screw plugs 35. Pressed into the bore is a bushing 36 havingalined bores 37 and 38 of different diameters. Abutting hollow plungers39 and 41 are fitted to and sli-dable in the alined bores, `37 and 38.Annular grooves 42, 43 and 44 are formed in the bushing surface and areconnected respectively with the groove 27 of valve 14, with thesurnp 13and with the valve 15 and groove 24 of valve 14. Plunger 39 carriesadjacent its open end a check valve 45 `which is biased closed vbyspring 46. Space 47 is connected with valve 15 and with groove 24 ofvalve 14. Plonger 39 has three sets of radial ports 4S, 49 and 50,formed therein. Spring 54 biases the plungers 39 and 41 to the positionshown. Pressure fluid in the groove 44 is admitted to the right ofplunger 41 by ports 52 in the stop 53. In the illustrated position ports5t) communicate with space 47; ports 48 register with the groove 42 andports 49 are obstructed. In the unloading position ports 50 areobstructed and ports 49 unload the pump 12 by direct ing tlow therefromto the sump 13 via groove 43.

The open center control vvalve 15 comprises a housing having a portedvalve bore 54 therein. A central annular groove 55 is formed in thefboreyand is connected with the sump 13 as shown. On each side of the groove55 are grooves 56 and `56 which each connect to inlet chamber 57 whichis connected with the grooves 24 and 44 and space 47. This -inletchamber 57 is also in communication with sump 13 through check valve `58which permits flow from the sump but inhibits reverse flo-W. Betweeneach o-f the grooves 56 and 56' and the corresponding end of the bore 54are 4grooves 59 and 59' which are connected with `the motor17.` A coredchamber 61 is formed in thehousingand is connected with the sump at alltimes. Arelief valve assembly is provided as generally indicated at 62.

A valve plunger 63 `is reciprocable in the bore 54 and is shiftableselectivelyto fthree positionsin each of `which animpositive detent 64is eiiective to holditagainst accidental movement.. Theiplungerisprovided with adjacent point. Between each of the grooves 65 and 65and the corresponding end of plunger 63 are encircling grooves 66 and 66which register, at all times, with Agrooves 59 and 59 respectively.Grooves 65 and 66 are connected by port 67, ports 65 and 66 aresimilarly connected by a port 67.

In the illustrated position the inlet chamber 57 and the motor connectedgrooves 59 and 59 are connected with the sump through grooves 65 and 65.When the plunger 63 is raised, inlet chamber 57 and grooves 56 and 59are connected together through port 67 and groove 59 is connected to thesump 13 through port 67 and groove 55. A reverse condition isestablished when plunger is in its lowermost position and the motor 17will rotate in the reverse direction. The open-center valve is generallyconventional, and no claims are directed to its construction.

In the drawings the parts are shown in the position assumed when theprime mover is idling and the vehicle is at rest or coasting. As shownpumps 11 and l2 are connected through valve 14 past needle valves 28with the sump 13. The pumps are also unloaded by valve 15. If Valve 1Sis shifted up or down to drive motor 17 either forward or backward asthe case may be, the pumps 11 and 12 initially remain unloaded. As primemover speed is increased plungers 19 and 21 will move toward each otherand will, respectively, connect pump 12 with groove 27 and the valve 16,and pump 11 with the groove 24 and inlet chamber 57 of valve 15. The twoneedle valves 28 are preferably dierently adjusted so that the pumps areloaded successively, pump 11 being the first loaded. This aords smootheroperation.

Under normal operating conditions when the load is not excessive thecheck valve 45 in valve 16 is open and both pumps 11 and 12 supply fluidto the inlet chamber 57 of open-center valve 15. The pressure in chamber57 is a direct function of the load on motor 17. This pressure acts onthe open ends of plungers 39 and 41. Plunger 39 is of a larger area thanplunger 41. It will be apparent that plungers 39 and 41 constitute adifferential piston motor which biases the plungers toward the rightwhen they are subject to pressure. This bias increases as the loadincreases. When it reaches a predetermined amount, the plungers 39 and41 will be shifted to the right against the bias of spring 54 therebyobstructing port S0 and opening port 49 whereby pump 12 kis unloaded.

When pump 12 is unloaded, pump 11 continues to operate against the sameback pressure. The vehicle will slow, but can be accelerated within thelimits established by the setting of the relief valve 62 and by themaximum speed of the prime mover. With pump 11 operating alone itsdischarge pressure may be further increased by accelerating the primemover. The maximum pressure attainable in the system is determined bythe setting of relief valve 62.

When the load is reduced the back pressure in the system is reduced andplungers 39 and 41 ofvalve 16 resume their illustrated position wherebypump 12 is again effective to supply iiuid to the system. It will beobvious that maximum speed is attained when both pumps are operatingunder a light load, whereas heavy loads can be handled, at a lowerspeed, by a single pump. The transition is smooth and automatic.

In addition to loading the pumps serially, the valve 14 serves a seconduseful purpose. It unloads the pumps when the prime mover is notoperating. Hence regardless of the position of valve 15, the prime moveris started without being initially subject to load.

The open-center control valve 15 has' a central float position in whichthe inlet chamber 57 is connected to the I sump as are the motorconnected grooves 59 and 59. This permits the vehicle to coastfreelywhen desired.

When the vehicle is being driven downhill and is permitted to coastwithout shifting the valve 15 to its midposition, the motor 17 willoperate as a pump and may displace more fluid than it is receiving frompumps 11 and 12. Check valve 58 will open under these conditions tosupply fluid to the motor inlet, whereby cavitation in the motor 17 isprevented. Check valve 58 could be replaced by two check valves, onebetween a sump conneetion, such as chamber 61, and each of the pipeconnections to the motor 17 from grooves 59 and 59'.

Figure 3 shows a modification of the valve 14. It comprises a body 101having a bore 102 therein. Opposite ends of bore 102 are closed by screwcaps 103 having threaded apertures which receive adjusting screws 104.Lock nuts 105 and protecting cap nuts 106 are provided on screws 104. Anabutment 107 is adjnstably mounted in each cap 103. Spring biasedagainst the grooved inner face of abutments 107 are hollow plungers 108and 109 which are reciprocable in bore 102. Adjacent ends of theseplungers are closed. A manifold sump connection 111 is connected to eachof the three encircling grooves 112, 113 and 114 formed in the boresurface. Threaded connections 115 and 116 are provided near oppositeends of bore 102 and may be connected respectively to pumps 11 and 12.An encircling groove 117 is provided between grooves 112 and 113 and maybe connected to valve 16. A corresponding groove 118 is located betweengrooves 114 and 113 and may be connected to valve 15. The plungers 108and 109 are provided with three sets of radial ports, 119, 120, and 121,and 119', 120 and 121. respectively.

In Figure 3 the valve is shown in the position it would assume when theprime mover is idling. As shown the ports 112 and 120 register as doports 114 and 120. This initial position of the ports may be adjusted bymoving abutments 107. In this way the throttling effect imposed on thefluid owing to the sump may be varied, whereby the shifting of thevalves to operating position when the prime mover is accelerated can becontrolled. As the back pressure to the left of plunger 109 increases,the plunger is shifted to the right to bring ports 119 and 117 intoregistry. Plunger 108 is shifted in a similar fashion. By adjustment ofthe abutments 107, the plungers 108 and 109 can be made to shiftserially in the order stated or in the reverse order. It is preferredthat plunger 108 shift firstas has already been pointed out inconnection with Figures 1 and 2.

It will be apparent the valve of Figure 3 may be .substituted for valve14 shown in Figure 1.

If desired the three valves 14, 15 and 16 can be built using a singlecast housing or body in which theppipe connections wouldv be replaced bycored passages. The design of such single valve housing is deemed to bewithin the skill of a person skilled in the art of valve constructionand is therefore not illustrated.

What is claimed is:

l. In a hydraulic transmission of the type including a prime mover, aplurality of pumps driven thereby and connected in parallel flowrelation between a sump and a control valve having a float position, andan unloader for one of said pumps serving to unload that pump wheneverthe pressure of the liquid supplied to said control valve exceeds aperdetermined maximum, the combination of a secondary unloader for eachof said pumps comprising a valve seat having an inlet connection from apump, an outlet connection to the control valve, and a restrictedunloading path connected with said sump; a

valve member; means biasing said member toward an initial position inwhich it interconnects said unloader path and said inlet from the pump;and motor means actuated by pressure in the inlet from said pump toshift said valve against said bias progressively toward a position inwhich it establishes communication between the inlet from said pump andsaid outlet connection, and closes said unloader path.

2. The combination defined in claim l in which the restrictionin each ofsaid unloaded paths is variable independently of the restriction in theother unloader path.

3. The combination dened in claim 1 in which the restriction in saidunloader path comprises an adjustable stop for said valve member andagainst which it is biased by said biasing means whereby theinterconnection between said unloader path and the inlet from said pumpmay be varied in size.

4. In an hydraulic system of the type including a pump, a motor and acontrol valve arranged to control the ow of liquid from said pump tosaid motor; an unloader valve for said pump comprising a valve seathaving a 10 supply port connected with the pump discharge, a dischargeport connected with the control valve and an eX- haust port connectedwith the sump; flow restricting means for said exhaust port; a portedvalve member biased toward an unloading position in which itinterconnects said supply and exhaust ports; motor means actuated inresponse to rising pressure in said supply port to urge said valvemember iu a direction to interconnect said supply and discharge portsand close said exhaust port.

5. The combination deiined in claim 4 in which the iiow restrictingmeans comprises an adjustable stop effective to limit the transversearca of the iiow path from the supply to the exhaust port in saidunloading position.

References Cited in the le of this patent l UNITED STATES PATENTS EamesMar. 6, 1956

